1. Field of the Invention
This invention relates to a multi-piece solid golf ball comprising a solid core and a cover of two inner and outer layers enclosing the solid core.
2. Prior Art
At present, golf balls of various structures have been proposed. A greater number of proposals are made on solid golf balls, especially multi-piece solid golf balls having a solid core enclosed with a cover of plural layers, so as to improve their travel distance, controllability or spin rate and feel when hit. See JP-A 4-244174, JP-A 6-142228, JP-A 7-24084, JP-A 7-24085, JP-A 9-10358, and JP-A 11-104273.
However, there is a desire to have a multi-piece solid golf ball having further improved flight performance, good spin properties, and a pleasant feel when hit with wood, iron and putter clubs as well as good scraping resistance and durability.
Making extensive investigations to meet the above demand, the inventor has found that a multi-piece solid golf ball comprising a solid core and a cover of two inner and outer layers enclosing the solid core and formed on the surface with a plurality of dimples is improved when the solid core in its entirety has a hardness distribution falling within the range of JIS-C hardness 50 to 85, the difference between maximum and minimum JIS-C hardnesses in the solid core falls within 5%, the cover inner layer has a JIS-C hardness of 70 to 90, the cover outer layer has a JIS-C hardness of 60 to 80, the sum of high-speed region dimple operative volumes HDOV of respective dimples is 170 to 310, the sum of low-speed region dimple operative volumes of respective dimples LDOV is 200 to 310, and the overall dimple volume is 260 to 360 mm3.
Specifically, the invention provides a multi-piece solid golf ball as defined below.
(1) A multi-piece solid golf ball comprising a solid core and a cover of two inner and outer layers enclosing the solid core and formed on the surface with a plurality of dimples, wherein the solid core in its entirety has a hardness distribution falling within the range of JIS-C hardness 50 to 85, the difference between maximum and minimum JIS-C hardnesses in the solid core falls within 5%, the cover inner layer has a JIS-C hardness of 70 to 90, the cover outer layer has a JIS-C hardness of 60 to 80, the sum of high-speed region dimple operative volumes HDOV of respective dimples is 170 to 310, the sum of low-speed region dimple operative volumes of respective dimples LDOV is 200 to 310, and the overall dimple volume is 260 to 360 mm3. mm3.
(2) The multi-piece solid golf ball of claim 1 wherein provided that (a) represents a surface JIS-C hardness of the core, (b) represents the JIS-C hardness of the cover inner layer, and (c) represents the JIS-C hardness of the cover outer layer, they satisfy the relationship: (a)xe2x89xa6(b)xe2x89xa7(c).
(3) The multi-piece solid golf ball of claim 1 or 2 wherein the solid core has a specific gravity of 1.0 to 1.3, the cover inner layer has a specific gravity of 0.8 to 1.2, and the cover outer layer has a specific gravity of 0.9 to 1.3.
(4) The multi-piece solid golf ball of any one of claims 1 to 3 wherein the cover inner layer and/or cover outer layer is mainly formed of a thermoplastic resin.
(5) The multi-piece solid golf ball of any one of claims 1 to 4 wherein the cover outer layer is mainly formed of a thermoplastic polyurethane elastomer obtained using an aromatic or aliphatic diisocyanate.
(6) The multi-piece solid golf ball of any one of claims 1 to 5 wherein the cover outer layer is mainly formed of the reaction product of a thermoplastic polyurethane elastomer with an isocyanate compound.
(7) The multi-piece solid golf ball of any one of claims 1 to 6 wherein the cover inner layer is mainly formed of an ionomer resin or an ionomer resin and an olefinic elastomer.
The golf ball of the invention has a stretching flight performance along a relatively low trajectory, an increased travel distance, ease of control on iron shots, and a pleasant feel when hit with wood, iron and putter clubs, and is resistant to scraping and durable upon control shots with an iron club.
The multi-piece solid golf ball of the invention gives a tight comfortable feel and good rebound owing to the hardness distribution of the entire core optimized by minimizing the difference between maximum and minimum JIS-C hardnesses in the hardness distribution of the core. Additionally, the relatively soft cover inner layer and the cover outer layer are properly combined and the dimples are optimized, and so the golf ball has the improved flight performance including a relatively low trajectory which is elongated near its fall, less sensitivity to wind when hit with a driver, and an increased run, satisfying the playability needed by players of varying head speeds.